The invention relates to a method for controlling the position of an actuator, in a manner whereby the position is adjusted adaptively. The invention is disclosed in the context of a method for controlling the position of an actuator which incorporates a servo valve and a servo drive wherein arrangements are made to connect the servo drive to a control device which is to be actuated in a fixed manner. It is possible to activate the servo drive by means of the servo valve. The servo drive is provided with a sensor which determines a change in a measured quantity (the actual value), as a function of a displacement of a movable piston in the servo drive. This change is fed back to a control unit.
German Offenlegungsschrift No. 2,233,851 discloses a method in which a control-slider is shifted by means of an electrical control unit which determines the difference between the actual value and the required value. Although, in these measurements, which are based on the difference between the required and actual values, steady-state control-deviations are admittedly avoided, the accompanying control-behaviour, namely the speed with which the actuator reacts to changes in the required value, is inadequate.
According to the invention, a method of the abovementioned type is provided for controlling the position of an actuator, in a manner whereby the position is adjusted adaptively, in which method the control-behaviour of the actuator is optimised, while minimising the control-deviations.
The method according to the invention permits the use of a servo valve which can be constructed with the aid of a modest precision-engineering effort, and which is amendable, despite the absence of any means of compensating-out the influences of varying operating conditions, to the adjustment of its actual characteristics-band in a manner whereby these characteristics are matched to a theoretical characteristic curve by means of an adaptation system which is economical to produce, and, as a result of this adjustment, optimum control is assured. The adaptation system according to the invention is more economical than the use of a precision-type servo valve.
According to the invention, a method of controlling the position of an actuator comprises the steps of generating a signal indicative of actuator position, generating a signal indicative of desired actuator position, comparing the actuator position signal to the desired actuator position signal, generating an error signal from the comparison, providing the error signal to a control unit, generating an adaptation signal in an adaptive system, generating a control signal in the control unit, combining the control signal with the adaptation signal to provide an adapted control signal, and providing the adapted control signal to the actuator to control it.
Illustratively, the step of providing the adapted control signal to the actuator comprises the step of supplying the adapted control signal to a triggering system, generating an actuator control signal in the triggering system and supplying the actuator control signal to the actuator to control it.
Further, in an illustrative embodiment, the step of generating an error signal comprises the step of subtracting one of the actuator position signal and desired actuator position signal from the other of such signals.
Additionally according to an illustrative embodiment, the step of generating an adaptation signal comprises the steps of providing the error signal to the adaptive system, generating a signum function in response to the error signal, providing the signum function to a summing point, integrating the signal from the summing point, operating on the integral with a hysteresis function, providing the result of the hysteresis operation to the summing point, and integrating the result of the hysteresis operation to provide the adaptation signal.
Alternatively, the step of generating an adaptation signal comprises the steps of providing the control signal to a model of the triggering system, generating in the triggering system model a model of the triggering system response to the control signal, comparing the model's response to the response of the triggering system, generating a second error signal based upon the comparison of the triggering system's response to the control signal and the model's response to the control signal, processing the second error signal in a parameter adjustment system to generate parameter adjustment signals, and providing the parameter adjustment signals to the model, and the step of combining the control signal with the adaptation signal to provide an adapted control signal comprises the step of providing the parameter adjustment signals to the control unit.
According to this alternative embodiment, the step of providing the parameter adjustment signals to the control unit comprises the steps of providing signals from the parameter adjustment system to a control unit modification system to generate the control unit parameter adjustment signals and providing the control unit parameter adjustment signals to the control unit.
According to another aspect of the invention, a method for adapting a control system comprises the steps of generating control system input errors, establishing a threshold error sign differential, above which threshold control system corrective action is indicated, determining whether errors of one sign predominate over errors of the other sign, comparing the predominance of errors of one sign over the other sign to the threshold, and generating an adaptation signal to the control system to take corrective action when the predominance exceeds the threshold.
According to an illustrative embodiment of the invention, the step of generating control system input errors comprises the steps of generating a desired value for the system being controlled, generating an actual value related to the current condition of the system being controlled, comparing the desired and actual values, and generating the control system input error.
Further according to this illustrative embodiment, the step of determining whether errors of one sign predominate over errors of the other sign comprises the step of assigning opposite signs to errors on opposite sides of the desired value.
Additionally according to this aspect of the invention, the step of determining whether errors of one sign predominate over errors of the other sign further comprises the step of integrating the signs of the errors.
According to this illustrative embodiment of the invention, the step of establishing a threshold error sign differential above which control system corrective action is indicated comprises the step of operating upon the integral of the error's signs with a hysteresis function.
Additionally, in this illustrative embodiment, the method includes the steps of maintaining the hysteresis function at its non-zero level until the integral of the signs of the errors goes to zero and subtracting one of the non-zero level of the hysteresis function and the assigned signs of the errors from the other of the non-zero level of the hysteresis function and the assigned signs of the errors to drive the integral of the signs of the errors to zero more rapidly.
Also in this illustrative embodiment, the step of generating a signal to the controllable system to take corrective action comprises the steps of integrating the non-zero level of the hysteresis function to generate the adaptation signal.
Additionally, in this illustrative embodiment, the method further comprises the step of generating an adapted control system output signal by subtracting one of the adaptation signal and the controllable system response to the input error from the other of the adaptation signal and the controllable system response to the input error.
Finally, this illustrative method further comprises the step of providing the adapted control system output signal to the apparatus controlled by the controllable system.
According to yet another aspect of the invention, an apparatus for controlling the position of an actuator comprises means for generating a signal indicative of actuator position, means for generating a signal indicative of desired actuator position, means for comparing the actuator position signal to the desired actuator position signal, means for generating an error signal from the comparison, means for providing the error signal to a control unit, means for generating an adaptation signal in an adaptive system, means for generating a control signal in the controller unit, means for combining the control signal with the adaptation signal to provide an adapted control signal, and means for providing the adapted control signal to the actuator to control it.
Additionally according to this aspect of the invention, the means for providing the adapted control signal to the actuator comprises means for supplying the adapted control signal to a triggering system, means of generating an actuator control signal in the triggering system and means for supplying the actuator control signal to the actuator to control it.
Further according to this aspect of the invention the means for generating an error signal comprises means for subtracting one of the actuator position signal and desired actuator position signal from the other of such signals.
Illustratively, according to this aspect of the invention the means for generating an adaptation signal comprises means for providing the error signal to the adaptive system, means for generating a signum function in response to the error signal, means for providing the signum function to an arithmetic point, means for integrating the signal at the arithmetic point, means for operating on the integral with a hysteresis function, means for providing the result of the hysteresis operation to the arithmetic point, and means for integrating the result of the hysteresis operation to provide the adaptation signal.
Alternatively, according to an illustrative embodiment, the means for generating an adaptation signal comprises means for providing the control signal to a model of the triggering system, means for generating in the triggering system model a model of the triggering system response to the control signal, means for comparing the model's response to the response of the triggering system, means for generating a second error signal based upon the comparison of the triggering system's response to the control signal and the model's response to the control signal, means for processing the second error signal in a parameter adjustment system to generate parameter adjustment signals, and means for providing the parameter adjustment signals to the model, and the means for combining the control signal with the adaptation signal to provide an adapted control signal comprises means for providing the parameter adjustment signals to the control unit.
According to this alternative, the means for providing the parameter adjustment signals to the control unit comprises means for providing signals from the parameter adjustment system to a control unit modification system to generate the control unit parameter adjustment signals and means for providing the control unit parameter adjustment signals to the control unit.
According to yet another aspect of the invention, an apparatus for adapting a control system comprises means for generating control system input errors, means for establishing a threshold error sign differential, above which threshold control system corrective action is indicated, means for determining whether errors of one sign predominate over errors of the other sign, means for comparing the predominance of errors of one sign over the other sign to the threshold, and means for generating an adaptation signal to the control system to take corrective action when the predominance exceeds the threshold.
Additionally according to this aspect of the invention the means for generating control system input errors comprises means for generating a desired value for the system being controlled, means for generating an actual value related to the current condition of the system being controlled, means for comparing the desired and actual values, and means for generating the control system input error.
Further according to this aspect, the means for determining whether errors of one sign predominate over errors of the other sign comprises means for assigning opposite signs to errors on opposite sides of the desired value.
Advantageously, according to an illustrative embodiment, the means for determining whether errors of one sign predominate over errors of the other sign further comprises means for integrating the signs of the errors.
Additionally according to this embodiment, the means for establishing a threshold error sign differential above which control system corrective action is indicated comprises means for operating upon the integral of the error's signs with a hysteresis function.
In accordance with an illustrative embodiment of this aspect, the apparatus further comprises means for maintaining the hysteresis function at its non-zero level until the integral of the signs of the errors goes to zero.
Additionally according to this illustrative embodiment, the apparatus further comprises means for subtracting one of the non-zero level of the hysteresis function and the assigned signs of the errors from the other of the non-zero level of the hysteresis function and the assigned signs of the errors to drive the integral of the signs of the errors to zero more rapidly.
Further according to this illustrative embodiment, the means for generating a signal to the control system to take corrective action comprises means for integrating the non-zero level of the hysteresis function to generate the adaptation signal.
Illustratively the apparatus further comprises means for generating an adapted control system output signal by subtracting one of the adaptation signal and the control system response to the input error from the other of the adaptation signal and the control system response to the input error.
Further, illustratively, the apparatus comprises means for providing the adapted control system output signal to the apparatus controlled by the control system.
Further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.